Grate fired fluid heating unit



Jan. 22, 1952 R. c. HUSTON GRATE FIRED FLUID HEATING UNIT 2 SHEETS-SHEET1 Filed March 6, 1948 INVENTOR {imp/ C Hus zon 01W ATTORNEY Jan. 22,1952 R. c. HUSTON CRATE FIRED FLUID HEATING UNIT Filed March 6, 1948ATTORNEY Patented Jan. 22, 1952 GRATE FIRED FLUID HEATING UN IT Ralph"C. Huston, Wadsworth, Ohio, assignor to The 'Babcock & Wilcox Company,Rockleigh, N..J., a corporation of New Jersey Application March 6, 1948,Serial'No.,13,369

7 Claims.

' l The present invention relates in general to the construction andoperation of a fluid heater having a grate-fired furnace, particularlywith ref- Hence to the disposition of fluidiheating surface associatedwith the :furnace walls.

In fluid heaters of the vapor generator or steam boiler classification,it is common practice to employ grate-fired furnaces having fluid cooledside walls in which rows of upright fluid conducting tubes are connected.to headers ar.-'

ranged marginally of the grate, make-up liquid being fed to the headersat intervals along their lengths. Such headers are necessarily ofrelatively large cross section and for the higher boiler operatingpressures are .necessarily of heavy wall thicknesses. When thick walledheaders are installed marginally of a grate, it is found that heatcracks often develop in header surfaces directly exposed to the burningbed of fuel, sometimes after onlylimited periods of service. This is dueto the high temperature gradient through i the thick header wall whichcauses the wall metal to become overheated. The effect is accentuatedwhen the furnace is operated under forced draft, .as a result of thehigher rtemperatures involved, and particularly when blow holes are.formed in thin areas of the bed and localized zones of intense heat arecreated, the risk of damage to metals adjacent the firing zoneordinariiy being increased when coals of a bituminous character are:employed.

A purpose of my invention therefore is to provide a grate .fired fluidheating unit .in which .fluid cooled furnace wall areas may bedirectlyeX- ,posed to the burning bed of fuel with a minimum risk of injury tothe metal of fluid conducting elements, irrespective of the character offuel being burned. I

. Another object pertainingmore particularly to the construction .of agrate fired fluid heater furnace, having fluid conducting elements ofrelatively large cross section marginally of the grate, is to provide afluid cooledmetallic barrier or shield betweensuch elements and the bedof fuel, the barrier to be formed of tubes .of relatively small crosssection so as to enable tubes having relatively thin walls to be usedfor a "given operating pressure as compared with the relatively thickwalled fluid'conducting elements "of larger cross section.

A further object isto arrange the tubularheat fbarrier'in such manner asto be more readily "renewable than the fluid cooled element shieldedthereby.

.An object is also to support the tubular barrier unit from theshieldedelement and to pro- .vide for the circulation of fluid therethrough inparallel-with the main circulatory system of the fluid heating unit.

The various features of novelty which characterize my'invention arepointed out with particularity in the claims annexed to and forming a'part'of this spectification. For a better understanding of theinvention, its operating advantages and specific objects attained by itsuse, reference should be had to the accompanying drawings anddescriptive matter in which I have :illustratedand describedselectedembodiments of my invention.

Of the drawings: Fig. 1 is .an elevational View in section of a sickerfired vapor generating unit including an illustrative embodiment of myinvention;

Fig. 2 is a partial vertical section of the unit shown in Fig. 1,-taken:along line 2-2;

Fig. 3 is a fragmentary detailed enlargement of Fig. :1 featuring thefluid-cooled structure ad jacent the grate;

Figs. 4, 5 and 5 are transverse .sections taken respectively along lines4-4, 5-5, and 6-6, of

Fig. 3; and

Fig. 7 is a fragmentary enlargement of Fig. 3, rotated through 90'.

The vapor generating unit as illustrated in Fig. 1 comprises a steamboiler of the bent tube type having its major convection heating surfaceprovided by banks of tubes I2, 13, [4 extending between and connected toan upper, steam and water drum l5 and a lower, muddrum .16, a

superheater ll havingsteam inlet connections ill from drum l5 beingdisposed between the front tube bank 12 and the intermediate tube bank43. A stoker'fired boiler furnace l9, having its combustion chamber 21arranged forwardly of the front boiler bank l2, is provided with fluidcooled boundary walls comprising side walls 23, of which one only isshown, airont wall -24, a rear wall 25, and a roof 26. The stoker firingapparatus includes a traveling chain grate 21 having its top run 28movable from front to rear across the bottom of combustionchamber 2i andreceiving coal or other solid fuel delivered thereto from stokerapparatus 29 arranged exmriorly of the furnace adjacent the lower end ofits front wall 24. Air for combustion is delivered under pressure insuitable known manner to the space between the upper and lower runs ofthe grate. A chain guide member 3i, or series of such members, isdisposed along each margin of the top run 23 and mounted in known manneron the grate supporting structure. An ash discharge hopper or pit 32 isprovided adjacent the rear end of the grate.

Furnace walls 23, 24 and 25 are cooled by fluid conducting tubes 23a,24a, and 25a, respectively, while the roof 26 is cooled by upperextended portions of the front wall cooling tubes 24a, and all furnacewall cooling tubes are connected into a natural circulatory system whichincludes boiler drums I and I6 in a manner hereinafter more fullydescribed.

A lower portion of front furnace wall 24 is inclined upwardly andrearwardly to provide an ignition arch 34 above a front portion of thegrate 21, while a lower portion of the rear furnace wall 25 is inclinedupwardly and forwardly to provide an arch 35 above a rear portion of thegrate, the arches 34 and 35 cooperating to define a throat passage 36 ofsmaller gas flow area than the combustion regions immediately upstreamand downstream thereof. A wall 31 extends from the upper end of reararch 35 to the lower boiler drum I6 to provide an outer boundary wallportion of the boiler tube space.

The front wall tubes 24a are connected at their lower ends to a header38 which extends horizontally above the grate 21, in upwardly spacedrelation thereto adjacent the lower end of the front ignition arch 34,the lower portions of tubes 24a extending upwardly adjacent the innerface of the arch and having their exposed surfaces protected by a layerof heat refractory material 39 applied thereto. The upper ends of tubes24a are connected to the upper boiler drum I5.

The rear wall tubes 25a are connected at their lower ends to a header 4Idisposed rearwardly of the grate 21, beyond the ash pit 32, andextending horizontally at an elevation below the top run of the grate,the header 4I having tubular make-up water connections 42 with the lowerboiler drum I6. The upper ends of tubes 250. are connected to the upperboiler drum I5 between the connections provided for the tubes of boilerbanks I2 and I3. The lower portions of tubes 25a extend upwardlyadjacent the inner face of the rear furnace wall 25 where they aredirectly exposed to furnace heat whereas, above the wall 25,intermediate portions 25b of these tubes are inclined rearwardly andupwardly to provide support for a bafiie 43 which defines,

with roof 25, a passageway 45 through which heating gases are directedinto contact with convection heated surfaces of the boiler andsuperheater. An upright bafiie 41, disposed adjacent the forward side oftube bank I3 and constituting an upper extension of baflie 43,terminates in downwardly spaced relation to the upper boiler drum I5 todefine an entrance for gases into the space containing tube banks I3 andI4, the gases discharging from the space through outlet 48.

In each side wall 23, a circular lower side wall header 56 extendshorizontally adjacent the top run 28 of the grate, each header 5!!having the lower ends of tubes 23a of the associated wall 23 connectedthereto, and having tubular makeup water connections 5! with the lowerboiler drum I6, the make-up connections or tubes 5| having their lowerends connected to the respective headers 50 at spaced intervalstherealong as indicated in Fig. 3. The upper ends of tubes 23a in eachside wall 23 are connected to an upper header 52 from which riser tubeconnections 53 extend to the upper boiler drum I5.

Each header 5!) is supported at intervals along its length by means ofsupport members 54 and 56 mounted on a plate 51 associated with the 4grate supporting structure. As shown, each member 54, adjacent therearward end of each header 50, is in the form of a rectangular platevertically aligned with the centerline of the header and having itsupper edge secured by welds 58 to the header and its lower edge securedby welds 59 to plate 51. 7 Each member 56, as shown, includes arectangular base plate portion 6I together with integral upright platelike portions 62 and 63 arranged at right angles to each other, theportion 62 being arranged longitudinally of header 50, in verticalalignment with the centerline thereof and having its straight upper edgesecured thereto by welds 64, and the portion 63 extending transverselyof the header and having its arcuate upper edge conforming to thecircular contour of the header and being secured thereto by welds 65.Each support member 56 is permitted to move relative to plate 51 inunison with the longitudinal movement of header 50, each base plateportion 6I being disposed between spaced guide bars 61 suitably securedas by welds 68 to plate 51. Each header 56 is thus free to expandforwardly from its point of stationary support on member 54 adj acentits rearward end.

Each lower side wall header 50 is shielded from contact with the movingbed of burning fuel on the grate by means of a group of tubes IIextending longitudinally of the header adjacent the furnace sidethereof, the tubes II being of relatively small diameter as comparedwith the diameter of a header 50, for example, in a ratio of an order ofabout 1:3. In each side wall 23, the header protecting tubes II havetheir intermediate length portions straight and parallel to each other,and also parallel to the header 50 with which each group is associated,these intermediate straight length portions also extending beyond therespective headers 50 at both ends. Tubes II have their rearward endportions bent downwardly and connected to the rear wall downtake header4|, and have their forward end portions bent upwardly and connected tothe front wall uptake header 3B. As thus connected, the tubes II receivewater fed from transverse header M and act as water supply tubes to thetransverse front header 38, a natural circulation through tubes II beinginduced by the head differential resulting from steam generation in thefront wall cooling tubes 24a which extend from the header 38 to thesteam and water drum I5.

The tubes II are arranged in groups of threes, for example, in thepattern indicated in Figs. 4, 5 and 6, with the lowermost tube of eachgroup resting on asbestos rope I2, or the like, received in a groove inthe upper edge of chain-guide 3|. As herein illustrated, each tube II isin contact with the tube next adjacent, while the uppermost tube isadditionally in contact with header 50. Tubes II are retained inposition adjacent each header 50 by means of tie bolts I3 having theirouter ends bent to engage tie loops I4 which are welded to therespective tubes II, and having their inner ends threaded and receivedin slots I5 in the respective angle members 16 which are arranged inlongitudinally spaced groups as shown in Fig. 3, with the members ofeach group secured to the headers 50 in longitudinally andcircumferentially spaced relation. The inner end of each bolt I3 isfitted with a nut I8 bearing against a washer I9 which is preferablytackwelded to the respective angle member I6 after the associated tubeII is tied in place. Although not illustrated. the outer bent end ofeach tie bolt 33 may be arranged at right angles to the body portion ofthe bolt and fitted with a nut to facilitate assembly and also toprevent disengagement from within the loop 14. Thus the tie bolts holdthe tubes H in predetermined parallel relationship to the furnace faceof the side wall header while providing for differential expansion withrespect thereto. The space between the assembled tubes H and each header59 and support plate '5'? is enclosed at its outer side by a platemember BI having its upper edge portion overlapping and secured to abar, or bars, 82 attached to header 50, the space thus enclosed beingfilled with loose asbestos 83, or the like, to provide a seal againstthe escape of furnace gases.

While in accordance with the provisions of the statutes I haveillustrated and described herein the best form of my invention now knownto me, those skilled in the art will understand that changes may be madein the form of the apparatus disclosed without departing from the spiritof the invention covered by my claims, and that certain features of myinvention may sometimes be used to advantage without a corresponding useof other features.

I claim:

1. In a furnace having a grate associated with the combustion chamberthereof, a fluid conducting header arranged marginally adjacent the fuelsupporting surface of said grate, a group of fluid conducting tubesparalleling said header at the side toward said grate, and means tyingsaid tubes to said header and maintaining successive tubes of said groupin contacting relationship.

2. In a furnace having a grate associated with the combustion chamberthereof, a fluid conducting header arranged marginally adjacent the fuelsupporting surface of said grate, a group of fluid conducting tubesarranged in vertical superj acent succession alongside of and parallelto said header at the side toward said grate, and means tying said tubesto said header and maintaining successive tubes of said group in saidsuperjacent relationship.

3. The combination as defined in 'claim 2 wherein the tying means isformed of separate components each having a connection to said headerand a connection to one of said tubes.

4. The combination as defined in claim 2 wherein the tying means isformed of separate components individually engaging one of said tubesand comprising a loop member secured to the tube and a tension memberhaving one end in engagement with said loop.

5. The combination as defined in claim 4 comprising a group of memberssecured to said header at circumferentially spaced positions forengagement by said tension member components.

6. In a furnace having a grate in the combustion chamber thereof, afluid conducting header associated with a wall of said chamber andextending marginally adjacent the fuel supporting surface of said grate,a group of fluid conducting tubes arranged longitudinally of said headerat the side adjacent said grate, said tubes being tied to said header bymeans holding said tubes in predetermined transverse relationship whilepermittin longitudinal movement thereof relative to said header, andmeans for supporting said header at longitudinally spaced points bymeans maintaining said header fixed at one of said points whilepermitting longitudinal movement thereof at other points therealong.

7. In a furnace having a combustion chamber defined in part by anupright wall arranged at one side of a grate extending across saidchambar, a fluid conducting header associated with said wall andextending longitudinally of said grate at an elevation adjacent the fuelsupporting surface thereof, a group of fluid conducting tubes arrangedat successive elevations alon the inner face of said header, means tyingsaid tubes to said header at spaced points therealong while permittinglongitudinal movement of said tubes relative to said header, and meansfor supporting said header at longitudinally spaced points by meansmaintaining said header fixed at one of said points while permittinglongitudinal movement thereof at other points therealong.

RALPH C. HUSTON.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS Number Name Date 1,456,649 Poppenhusen May 29,1923 1,456,650 Poppenhusen May 29, 1923 1,999,984 Bailey et al Apr. 30,1935 2,005,082 Greenawalt June 18, 1935 2,159,557 Heller May 23, 19392,186,919 Bailey Jan. 9, 1940 2,196,889 Bailey Apr. 9, 1949 2,250,536Kennedy July 29, 1941 2,333,078 Wallis et al Oct. 26, 1943 2,333,644Ebbets et al Nov. 9, 1943 2,412,568 Donahue et a1 Dec. 17, 1946 FOREIGNPATENTS Number Country Date 109,565 Australia Jan. 25, 1940 500,882Great Britain Feb. 16, 1939

